Pins and pin-like cylindrical parts are frequently used in stationary mounted "in-factory" machines and in mobile machinery to secure certain machine components to one another. One type of application for such pins involves "linking" two components together in a way that one is relatively movable with respect to the other. Rotating crank arms pinned to stationary structures are but one example. A piston-type engine as in most automobiles uses a pin to connect a reciprocating piston head with a connecting rod which not only reciprocates with the head but which also rotates through a few degrees with respect to such head.
In what might be termed small scale machines (an auto engine, for example), pin retention is by a cotter key or other type of known retainer. However, with larger machines, pin retention can be and often is a substantial design problem. Nowhere is this more true than in large mobile machines such as earth-moving and earth-excavating machinery.
Such machinery is available in a wide variety of types ranging from the familiar rubber-tire mounted and crawler-mounted to the less-common dragline. A dragline is often used for removing top soil and "overburden" to expose a valuable mineral, e.g., coal, beneath but near the earth's surface.
Draglines are equipped with an angularly-extending boom from which is suspended a "bucket" having an open mouth and digging teeth, both toward the main portion of the machine. Overburden is removed by placing the bucket on the ground at a point distant from the machine and pulling it toward the machine, filling the bucket in the process. Once filled, the machine pivots about a central axis and the bucket emptied at a spoil pile somewhat away from the area being excavated.
Smaller draglines are crawler mounted (much like a military tank) and capable of movement in the same way albiet at much slower speeds. However, as draglines (and their digging buckets) increased in size, crawler mounting was found to be impractical and in the early 1900's, the "walking" dragline was developed. The walking dragline is so named because it takes short "steps" and uses a "walk leg" mechanism (which resembles a human leg) to do so. A difference is that in a walking dragline, both legs step simultaneously.
To give some perspective to the following discussion, a large walking dragline--made by Harnischfeger Industries of Milwaukee, Wisconsin, and incorporating the invention--has a main housing portion (including the machinery deck, operator's cab and the like) which is about 105 feet long, about 80 feet wide, about 40 feet high and weighs about nine million pounds. The boom extends about 300 feet and the capacity of the digging bucket is about 80 cubic yards. The walk legs of such dragline take steps about seven feet in length.
At least because of its size, weight and complexity, several problems attend draglines of earlier configuration. One is that such machines are usually used in remote sites and replacement parts are difficult to deliver and, because of their size and weight, even more difficult to install. Another is that the machine is shipped in pieces to the site and erected there. While certain types of relatively "loose tolerance" machining equipment are available to facilitate machine assembly (which can take several months), close tolerance machining equipment is not available, at least not readily so.
Wear cannot be avoided in any device having relatively moving parts but the efforts of earlier designers of draglines have not been entirely successful in reducing the effect of wear. For example, some known draglines are configured so that wear between parts involved at least one expensive, heavy, hard-to-replace part. And while such parts have been relatively durable and in many cases last for years, repair is accomplished only at great expense for the purchased part and at extended downtime. A machine like a walking dragline represents an enormous capital investment and working "uptime" must be maximized.
Yet another difficulty with earlier draglines is that they were sometimes designed and built with "loose" clearances where close or "zero clearance" construction would have been preferred. In the alternative, small clearances were used where indicated and the necessary close-tolerance machining was undertaken in the field at great expense and, on occasion, with questionable results.
As will become apparent, the invention resolves some of these difficulties in unique and imaginative ways.